How do people become pychotic?

In the wake of tragedy, I think everyone asks: Why? How did he get to be that way?

I like to think babies are not born psychotic. But could they be born with mental illness? And without proper care, it can turn into something serious?

Are people products of their environment? I think a person's upbringing has a lot to do with how they turn out. Children of poverty have more obstacles to overcome.

Are parents 100% to blame for how their child turns out? Our job as parents is to mold children into who they should become, teach them right from wrong, teach respect and kindness. But sometimes even despite our best efforts, they turn out differently. Are parents still to blame? Should they have noticed something sooner? I think all parents should be aware of what their children are doing. No one becomes psychotic overnight. I think it takes years.